Global Systematic Review with Meta-analysis Shows Responses of Forest Greenhouse Gas Emissions under Single Nitrogen, Single Phosphorus, or Interactive Nitrogen and Phosphorus Addition

Abstract

Increasing nitrogen (N) and phosphorus (P) deposition influences primary forest soil properties related to C and N dynamics, which may significantly affect greenhouse gas (GHG) emissions. We examined how the fertilization pattern and variation in soil in forest types can affect GHG emissions. We conducted a global systematic review of 66 publications on GHG emissions, pH, and C and N soil properties to examine the mechanisms underlying GHG emissions under N, P, and N×P additions in diverse forest ecosystems. The results of our meta-analysis showed that N and N×P addition considerably promote nitrous oxide (N₂O) emissions in tropical forests, and P addition insignificantly decreased N₂O emissions. N addition and P addition inhibit CO₂ emissions in subtropical forests, which contributes to C storage, although the latter effect was nonsignificant, and P addition increases C dioxide emissions in tropical forests. Moreover, additions of N and N×P promote and inhibit overall methane uptake in the variety of forests studied, respectively. Additionally, the results indicated that the form, rate, duration, and N: P ratio of fertilization and the mean annual precipitation and mean annual temperature are influential variables affecting GHG emissions from forests under the various fertilizer additions. Our results highlight that when accurately predicting the effect of N and P deposition on soil GHG emissions, the characteristics of different forest types should be synthetically considered, such as experimental conditions, environmental variables, and soil properties. These results advance the understanding of the responding mechanism of soil GHG emissions in forests to different N and P addition models.